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Tempering and what it means to 'draw it'

  1. Mar 8, 2012 #1
    HI. So I feel I have a pretty basic but good understanding of quenching and tempering processes (talking about steels). Tempering as I understand it removes internal stresses, reducing the hardness and brittleness created during quenching, but increasing other properties like toughness. (it can get sticky here dealing with the different adjectives such as hardness, toughness, strength, etc.) But mainly I'm focusing on the reduction of hardness and brittleness.

    So what happened is I read a book talking about tools - possibly not a completely reliable source but I don't know - and it said this "hammer heads are tempered during manufacture to withstand impact, though that hardness can also make them brittle."

    This statement seems to go against my understanding of temper. My only thought is that perhaps the author means to imply that the specific tempering process for hammer heads is such that they are left hard and brittle (i.e. a low tempering temp after a quench).
    It also in a latter section says: "never put a tool head in a fire to burn out [broken] handle wood. The wood may disappear, but so will the temper of the metal, making the tool brittle and dangerous to use." I can only imagine that instead of 'brittle' the author means that the steel loses some other impact quality that may allow it to chip. Or that it has reached some temperature where brittleness in reintroduced (I have read that there are a few 'zones' in tempering that actually reintroduce brittleness rather than reduce it.

    And lastly, a question I've long had hanging in the head: When people speak of 'drawing a blades temper' due to over-heating (such as on a grinding wheel) does this simply mean that the metal has been heated above the initial tempering temperature thereby making it softer than intended?

    Any words of knowledge and experience much appreciated.
  2. jcsd
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